Galileo's Lunar Observation

In 1610, Galileo dated his first letter describing telescopic observations
in which he saw the moon's cratered surface using his twenty-powered spyglass.
He wrote, “... it is seen that the Moon is most evidently not at all of an even,
smooth, and regular surface, as a great many people believe of it and of the
other heavenly bodies, but on the contrary it is rough and unequal. In short it
is shown to be such that sane reasoning cannot conclude otherwise than that it
is full of prominences and cavities similar, but much larger, to the mountains
and valleys spread over the Earth's surface.” Galileo went on to describe the
phenomena in considerable detail, rehearsing, as it were, the observations and
conclusions he was to publish more elaborately a few months later in
Sidereus Nuncius.